In a known configuration of a reduction gear for decelerating rotation of a motor or the like and amplifying torque, a gear is held by a carrier (e.g., see Patent Documents 1 and 2). In a configuration recited in Patent Document 1, a speed reduction mechanism (20) has a small gear (43), a large gear (42), a crank mechanism member (27), an external tooth gear (23), a support body (25), and an internal tooth gear body (21).
Output of a motor (10) is decelerated due to meshing between the small gear (43) and the large gear (42). Rotation of the large gear (42) is transmitted to the external tooth gear (23) via the crank mechanism member (27). The external tooth gear (23) has a plurality of external teeth and meshes with the internal tooth gear body (21) via a pin. The number of teeth of the internal tooth gear body (21) is slightly different from the number of teeth of the external tooth gear (23). As a result, when the crank mechanism member (27) rotates once, the external tooth gear (23) changes its angle by several degrees, and the rotation transmitted from the crank mechanism member (27) is decelerated. This rotation of the external tooth gear (23) is transmitted to the support body (25).
The support body (25) is coupled to a pinion (35) in a state of being supported by the internal tooth gear body (21) via a bearing (24a). In the configuration recited in Patent Document 1, external teeth formed on the outer circumference of an end of the support body (25) mesh with internal teeth formed on the inner circumference of the pinion (35). Thus, the output of the speed reduction mechanism (20) is transmitted from the support body (25) to the pinion (35). The pinion (35) further transmits a motive power by meshing with another gear.